When I play game the phone is warming around 30C, also it happens when I use maps and camera. I dont know how to fix it.
Nothing needs fixing.
Like any electronic item it will get warm in use, especially using GPS functions or graphically intensive apps.
The phone has its own internal temperature gauge and will warn you if it gets too hot and needs to cool down, however this is rare. I've never seen such a warning in 5 years of iOS device usage.
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